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Measurement of spin‐lattice relaxation times and chemical exchange rates in multiple‐site systems using progressive saturation
Author(s) -
Galbán Craig J.,
Spencer Richard G.
Publication year - 2007
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21185
Subject(s) - saturation (graph theory) , spin–lattice relaxation , nuclear magnetic resonance , condensed matter physics , lattice (music) , materials science , chemistry , physics , paramagnetism , mathematics , acoustics , combinatorics
A new method for measuring spin‐lattice relaxation times and chemical exchange (CE) rate constants in multiple‐site exchanging systems is described. The method, chemical exchange and T 1 measurement using progressive saturation (CUPS), was applied to determine T 1 s and analyze phosphorus exchange among phosphocreatine (PCr), ATP, and inorganic phosphate (Pi), mediated by creatine kinase (CK) and ATP synthase, using 31 P‐MRS. Two‐site exchange was analyzed in vitro and in the rat leg, and three‐site exchange was analyzed in the rat heart. Data were fitted to a model of progressive saturation incorporating T 1 relaxation and CE. For the in vitro system at 8.45T, we found T 1 (PCr) = 2.86 s and T 1 (γ‐ATP) = 1.72 s. For the rat gastrocnemius at 1.9T, we found T 1 (PCr) = 6.60 s and T 1 (γ‐ATP) = 2.06 s. For the rat heart at 9.4T, we found T 1 (PCr) = 3.35 s, T 1 (γ‐ATP) = 0.69 s, and T 1 (Pi) = 1.83 s. All of these values were within 20% of literature values. Similarly, the determined exchange rates were in the same range as published values. Using simulations, we compared CUPS with transient saturation transfer as a method for measuring T 1 s and rates. The two methods showed similar sensitivity to noise. We conclude that CUPS is a viable alternative for measuring T 1 s and CE rates in exchanging systems. Magn Reson Med 58:8–18, 2007. © 2007 Wiley‐Liss, Inc.